Method for determining reserved tones and transmitter for performing papr reduction using tone reservation

ABSTRACT

A method of determining reserved tones to be used for reduction of a peak to average power ratio (PAPR) of a signal includes: randomly selecting carrier indices for the reserved tones and generating a kernel signal based on the randomly selected carrier indices for the reserved tones; calculating a comparison reference average value of the kernel signal, comparing the calculated comparison reference average value with a prestored comparison reference average value, and preliminarily determining carrier indices of the reserved tones based on the comparison; re-arranging an order of the preliminarily determined carrier indices of the reserved tones; calculating comparison reference average values of kernel signals generated by changing each of the re-arranged carrier indices of the reserved tones, and finally determining carrier indices of the reserved tones which generate a kerneal signal having the smallest comparison reference average value among the comparison reference average values as indices of the reserved tones.

CROSS-REFERENCE TO THE RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application No.62/172,855 filed on June 9, 2015 and U.S. Provisional Application No.62/209,516 filed on Aug. 25, 2015, and Korean Patent Application No.10-2016-0016406 filed on Feb. 12, 2016, the disclosures of which areincorporated herein by reference in their entirety.

BACKGROUND

1. Field

Apparatuses and methods consistent with the exemplary embodiments of theinventive concept relate to a method of determining reserved tones and atransmitter performing peak to average power ratio (PAPR) reductionusing tone reservation, and more particularly, to a transmitterdetermining carrier indices reserved for PAPR reduction and performingPAPR reduction using tone reservation.

2. Description of the Related Art

Recently, broadcast and communication services become multi-functionaland wideband high quality. Also, in accordance with the development ofelectronic technologies, various broadcast receiving devices such as ahigh-definition digital television, a high specification smartphone, andthe like have been introduced and increasingly used. As a result, thedemand on various receiving methods and various service supports forbroadcast services has been increased.

Meanwhile, many transmitting and receiving systems provide broadcastservices through an Orthogonal Frequency Division Multiplexing (OFDM)scheme. Since the OFDM scheme performs data transmission using aplurality of carriers (or sub-carriers) in a predetermined frequencyband, it may transmit data at high speed and has characteristics that itis strong against multipath fading.

However, in the OFDM scheme, a transmission signal occasionally has alarge peak-to-average power ratio (PAPR). Data is transmitted throughmulti-carriers by performing Inverse Fast Fourier Transform (IFFT) on asignal of a frequency domain. Here, a size of an amplitude of an OFDMsignal may be represented by a sum of amplitudes of the multi-carriers.Therefore, in the case where phases of the multi-carriers are the same,an OFDM signal having a high maximum value is generated, whichrepresents a very high PAPR.

An OFDM signal having a very high PAPR deteriorates efficiency of a highpower amplifier and the high power amplifier is operated in a non-linearregion out of a linear operation range thereof, and thus, the OFDMsignal is distorted. Accordingly, there is a problem that performance ofa transmission and/or reception system is degraded. As a result,research into a method for reducing the PAPR is requested.

SUMMARY

Exemplary embodiments of the inventive concept may overcome the aboveproblem and other disadvantages not described above. However, theexemplary embodiments are not required to overcome the disadvantagesdescribed above, and may not overcome the above problem described above.

The exemplary embodiments provide a method of determining carrierindices reserved for PAPR reduction, and also provide a transmitter ofperforming the PAPR reduction using the reserved carrier indices.

According to an exemplary embodiment, there is provided a method ofreducing a PAPR of an input signal which may include: selecting aplurality of sets of indices of carriers to which a tone reservationsignal is to be allocated; performing IFFT on carriers of each of theplurality of sets of indices to generate a plurality of output signalseach of which includes a plurality of peak signals in a time domain;comparing averages of a predetermined amplitude range of the pluralityof output signals one another; determining a set of indices, among theplurality of sets of indices, of which carriers generates an outputsignal, among the plurality of output signals, having the smallestaverage of the predetermined amplitude range by the performing IFFT, asindices of carriers to which the tone reservation signal is to beallocated; and allocating the tone reservation signal to carriers of thedetermined set of indices to reduce the PAPR of the input signal.

According to an exemplary embodiment, there is provided a method ofdetermining reserved tones to be used for reduction of a peak to averagepower ratio (PAPR) of a signal. The method may include: randomlyselecting carrier indices for the reserved tones and generating a kernelsignal based on the randomly selected carrier indices for the reservedtones; calculating a comparison reference average value of the kernelsignal, comparing the calculated comparison reference average value witha prestored comparison reference average value, and preliminarilydetermining carrier indices of the reserved tones based on thecomparison; re-arranging an order of the preliminarily determinedcarrier indices of the reserved tones; calculating comparison referenceaverage values of kernel signals generated by changing each of there-arranged carrier indices of the reserved tones to another carrierindex, and finally determining carrier indices of the reserved toneswhich generate a kernel signal having the smallest comparison referenceaverage value among the comparison reference average values as carrierindices of the reserved tones to be used for the reduction of the PAPR.

In the generating the kernel signal based on the randomly selectedcarrier indices for the reserved tones, the kernel signal may begenerated by randomly selecting carrier indices for the reserved tonesamong carrier indices other than carrier indices into which a pilot isinserted, inserting one (1) into carriers of the randomly selectedcarrier indices, and performing IFFT on the carriers into which one (1)is inserted.

The comparison reference average value of the kernel signal may be anaverage value of amplitudes of peak signals satisfying a predeterminedcondition, except a peak signal having the greatest amplitude, among theplurality of peak signals of the kernel signal.

The predetermined condition may be a condition that the peak signalsbelong to a predetermined top range of amplitude except the peak signalhaving the greatest amplitude and another predetermined top range ofamplitude based on an amplitude of a peak signal having thesecond-largest amplitude, among the plurality of peak signals of thekernel signal.

In the preliminarily determining the carrier indices of the reservedtones, a smaller comparison reference average value among the calculatedcomparison reference average value and the prestored comparisonreference average value may be compared with a preset value, and carrierindices for a kernel signal having the smaller comparison referenceaverage value which is smaller than the preset value is preliminarilydetermined as the indices of the reserved tones.

The comparison reference average values may be calculated bysequentially changing respective carrier indices included in there-arranged carrier indices of the reserved tones to other carrierindices where a pilot is not positioned and the preliminarily determinedreserved tones are not positioned.

According to an exemplary embodiment, there is provided a transmitterfor reducing a PAPR of an input signal which may include at least oneprocessor to implement: a frame generator which generates a framecomprising a plurality of symbols; a pilot inserter which inserts aplurality of pilots into the symbols; a PAPR reducer which selects aplurality of sets of indices of carriers to which a tone reservationsignal is to be allocated such that the selected indices of carriers donot overlap indices of carriers to which the pilots are inserted; and anIFFT unit which performs IFFT on carriers of each of the plurality ofsets of indices to generate a plurality of output signals each of whichincludes a plurality of peak signals in a time domain, wherein the PAPRreducer compares averages of a predetermined amplitude range of theplurality of output signals one another, and determines a set ofindices, among the plurality of sets of indices, of which carriersgenerates an output signal, among the plurality of output signals,having the smallest average of the predetermined amplitude range by theIFFT unit, as indices of carriers to which the tone reservation signalis to be allocated, and wherein the PAPR reducer allocates the tonereservation signal to carriers of the determined set of indices toreduce the PAPR of the input signal.

According to an exemplary embodiment, there is provided a transmitterwhich may include: a frame generator configured to generate a frameincluding a plurality of OFDM symbols having a Fast Fourier Transform(FFT) size of 8K; a pilot inserter configured to insert a pilot intofirst carriers of the plurality of OFDM symbols, respectively; and aPAPR reducer configured to insert a signal for reducing a PAPR intosecond carriers reserved in at least one of the plurality of OFDMsymbols into which the pilot is inserted, wherein the second carriershave carrier indices defined as in Table 4 or 5.

The frame may include a preamble symbol, subframe boundary symbols, anddata symbols.

The second carriers may have the carrier indices defined in Table 4,when a position in the preamble symbol into which a preamble pilot is tobe inserted and a position in the subframe boundary symbols into which asubframe boundary pilot is to be inserted are defined based on a pilotinsertion pattern (Dx=6, 8, 12, 16, 24, 32), and an edge pilot is to beinserted into a first carrier and a last carrier in each of the subframeboundary symbols, and Dx is a difference of carrier indices betweenadjacent carriers into which the pilot is to be inserted.

The second carriers may have the carrier indices defined as in Table 4,when a position in the data symbols into which a scattered pilot is tobe inserted is defined based on a pilot insertion pattern (Dx=3, 4, 6,8, 12, 16, 24, 32 and Dy=2, 4) and an edge pilot is to be inserted intoa first carrier and a last carrier in each of the data symbols, and Dxis a difference of carrier indices between adjacent carriers into whichthe pilot is to be inserted, and Dy is a difference of symbol indicesbetween successive pilots on a specific carrier.

According to an exemplary embodiment, there is provided a receiver whichmay include: a receiver configured to receive a frame transmitted from atransmitter, a reserved tone remover configured to remove reserved tonesfrom a plurality of OFDM symbols constituting the frame, and a signalprocessor configured to process the plurality of OFDM symbols from whichthe reserved tones are removed, wherein carriers to which the reservedtones are allocated have carrier indices defined as in Table 4 or 5.

According to various exemplary embodiments, when PAPR reduction isperformed, it is possible to prevent a new peak from occurring, therebymore efficiently reducing a PAPR.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects of the exemplary embodiments will be moreapparent by describing certain exemplary embodiments of the inventiveconcept with reference to the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a method for reducing PAPR according toan exemplary embodiment;

FIG. 2 is a diagram illustrating a problem that is able to occur whenPAPR is reduced, according to an exemplary embodiment;

FIG. 3 is a diagram illustrating a frame structure according to anexemplary embodiment;

FIGS. 4 to 9 are diagrams illustrating a method for determining reservedtones according to an exemplary embodiment;

FIG. 10 is a flowchart illustrating the method for determining reservedtones according to an exemplary embodiment;

FIG. 11 is a block diagram illustrating a configuration of a transmitteraccording to an exemplary embodiment;

FIG. 12 is a block diagram illustrating a configuration of a receiveraccording to an exemplary embodiment; and

FIG. 13 is a flowchart illustrating a method in which the transmitterreduces PAPR using reserved tones according to an exemplary embodiment.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Hereinafter, the exemplary embodiments of the inventive concept will bedescribed in more detail with reference to the accompanying drawings.

The exemplary embodiments relate to a method for reducing a PAPR using atone reservation (TR) scheme, in a system in which a signal istransmitted by an OFDM scheme. Particularly, according to the exemplaryembodiments, in order to efficiently reduce a PAPR while avoidingcollision with pilots by considering positions of carriers in which thepilots exist in an OFDM symbol, carriers of specific positions are usedas reserved tones.

First, a method for reducing a PAPR according to a tone reservationmethod is as follows. In the tone reservation method, tones are reservedfor some of carriers. Here, the reserved tones do not transmit data andare used to reduce a PAPR. In this case, since a receiver neglects thereserved tones which do not transmit data and restores the data onlyfrom a signal at a tone position of data, there is an advantage that astructure of the receiver is simple.

Meanwhile, in the tone reservation method, a gradient algorithm is usedto reduce a peak. Hereinafter, a method for reducing a peak using thegradient algorithm will be described in more detail with reference toFIG. 1.

FIG. 1 illustrates a configuration diagram of a transmitter whichreduces a PAPR using the tone reservation method.

Referring to FIG. 1, reserved tones 10 and data (i.e., broadcast data,an L1 signaling including signaling information about the broadcastdata, pilots, etc.) 20 are input to a tone reserver 30, and a tonereservation signal is allocated by the tone reserver 30 to apredetermined carrier position known between a transmitter and areceiver by the tone reserver 30.

Meanwhile, if a sum of the reserved tones 10 and the input data 20 isinput to an Inverse Fast Fourier Transform (IFFT) unit 40, IFFT isperformed, and thereafter, an output signal x of a time domain isgenerated by a parallel/serial (P/S) converter 50. In this case, a peakreducer 60 reduces a PAPR of the output signal x.

The peak reducer 60 generates a kernel signal having impulsecharacteristics using the reserved tones. Here, the kernel signal isused to clip the output signal x.

Specifically, the peak reducer 60 detects a peak of the output signal x.That is, the peak reducer 60 detects a position, an amplitude, and aphase of the peak of the output signal x. In addition, in order toreduce the peak of the output signal x, the peak reducer 60 performs atleast one of circular shifting, scaling, and phase rotation on thekernel signal based on the position, the amplitude, and the phase of thepeak of the output signal x, and then adds the results to the outputsignal x.

Thereafter, the peak reducer 60 calculates the PAPR of the output signalx having a reduced peak. In addition, if the calculated PAPR does notmeet a target (or a desired) PAPR level, the peak reducer 60 may repeatthe above-mentioned process until the PAPR for the output signal x meetsthe target PAPR level, or may repeat the above-mentioned process as manyas the number of times (e.g., N) predefined by a system.

As such, according to a tone reservation method, the peak of a datasignal is reduced by adding the kernel signal to the data signal.However, as the kernel signal is added to the data signal, a new peakmay also occur in the data signal. Here, the data signal may be an OFDMsignal

For example, as illustrated in FIG. 2, when IFFT is performed in afrequency domain after 1 (one) is inserted into carriers to whichreserved tones are allocated, a kernel signal having a peak at aparticular time point in a time domain may be generated.

In this case, if the kernel signal is added to the data signal, a peakof the data signal may be reduced by a first peak, i.e., the greatestpeak of amplitude, of the kernel signal. However, since other portionsexcept the first peak are added to the data signal, when amplitudes ofthe other peaks except the first peak are large, a new peak may occur inthe data signal by the other peaks.

Therefore, according to an exemplary embodiment, the positions ofreserved tones (i.e., carrier indices used for the reserved tones) whichmay minimize the amplitudes of the other peaks of the kernel signalexcept the first peak of the kernel signal are determined, and thesecarrier indices are used as the reserved tones in order to reduce a PAPRof the data signal.

Hereinafter, a method of determining carrier indices in which tones arereserved according to an exemplary embodiment will be described.

First, according to an exemplary embodiment, since a signal istransmitted through a frame defined in an Advanced Television SystemCommittee (ATSC) 3.0 standard, a frame structure defined in the ATSC 3.0standard will be described with reference to FIG. 3.

According to the ATSC 3.0 standard, as illustrated in FIG. 3, the frameincludes a bootstrap 310, a preamble 320, and one or more subframes330-1, . . . , 330-n.

Specifically, the bootstrap 310 is positioned at a start of each frame,the preamble 320 is positioned following the bootstrap 310, and the oneor more subframes 330-1, . . . , 330-n are positioned following thepreamble 320.

The bootstrap 310, the preamble 320, and the one or more subframes330-1, . . . , 330-n comprise one or more OFDM symbols, and the numberof carriers for each OFDM symbol may be determined depending on an FFTmode (i.e., in an FFT size, the FFT size may be 8K).

Meanwhile, each subframe may include subframe boundary symbols and datasymbols. The subframe boundary symbols are positioned at boundaries withother subframes, and the data symbols are positioned between thesubframe boundary symbols. That is, a first OFDM symbol and the lastOFDM symbol among the OFDM symbols configuring each subframe are thesubframe boundary symbols, and the remaining OFDM symbols other than thesubframe boundary symbols are the data symbols.

Meanwhile, according to the ATSC 3.0 standard, pilots are inserted intothe preamble and the subframes for channel estimation andsynchronization.

Types of pilots inserted into the preamble and the subframes are asillustrated in the following Table 1.

TABLE 1 Symbol Preamble Scattered Subframe Continual Edge Type PilotPilot Boundary Pilot Pilot Pilot Preamble ✓ ✓ Data ✓ ✓ ✓ Subframe ✓ ✓ ✓Boundary

Referring to Table 1, a preamble pilot is inserted into the preamble, ascattered pilot (SP) is inserted into the data symbol, and a subframeboundary pilot is inserted into the subframe boundary symbol. Inaddition, a continual pilot (CP) is inserted into the preamble symbol,the data symbol, and the subframe boundary symbol, and an edge pilot isinserted into the data symbol and the subframe boundary symbol.

Meanwhile, a position into which a pilot is to be inserted may bedefined by an index of a carrier into which the pilot is to be inserted,or may be determined based on specific pilot patterns (e.g., Dx and Dy).Here, Dx means a difference in carrier index between adjacent carriersinto which a pilot is to be inserted, in a frequency direction (inregard to this, in ATSC 3.0, defined as separation of pilot bearingcarriers (that is, in the frequency direction), and in Digital VideoBroadcasting-Terrestrial Version 2 (DVB-T2), defined as difference incarrier index between adjacent scattered-pilot-bearing carriers), and Dymeans a difference of the number of symbols between successive pilots ona specific carrier, in a time direction (in regard to this, in ATSC 3.0,defined as number of symbols forming one scattered pilot sequence (timedirection), and in DVB-T2, defined as a difference in symbol numberbetween successive scattered pilots on a given carrier).

First, the position into which the preamble pilot is to be inserted maybe determined based on Dx. In the case of preamble pilot, since Dy is 1(Dy=1), the preamble pilot is inserted to the same position of everypreamble symbol. Specifically, the preamble pilot may be inserted intocells (i.e., carriers) having a carrier index k satisfying k mod Dx=0 inthe preamble symbol. Here, Dx may be 3, 4, 6, 8, 12, 16, 24, and 32, andthe system may select one of these values depending on a channelenvironment.

The position into which the scattered pilot is to be inserted may bedetermined based on Dx and Dy. Specifically, the scattered pilot may beinserted into a carrier having an index k in a first OFDM symbolsatisfying following mathematical expression 1.

k mod(D _(X) D _(Y))=D _(X)(I mod D _(Y))   (1)

Here, Dx and Dy may be defined as illustrated in following Table 2, andSPa_b means a pilot pattern, which a is Dx (a=Dx) and b is Dy (b=Dy).

TABLE 2 Pilot Pattern D_(x) D_(y) SP3_2 3 2 SP3_4 3 4 SP4_2 4 2 SP4_4 44 SP6_2 6 2 SP6_4 6 4 SP8_2 8 2 SP8_4 8 4 SP12_2 12 2 SP12_4 12 4 SP16_216 2 SP16_4 16 4 SP24_2 24 2 SP24_4 24 4 SP32_2 32 2 SP32_4 32 4

Meanwhile, the system may select one of SPa_b defined in Table 2depending on the channel environment.

A position into which a subframe boundary pilot is to be inserted may bedetermined based on Dx. Specifically, the subframe boundary pilot may beinserted into cells having a carrier index k satisfying k mod Dx=0 inthe subframe boundary symbol (except when k=0 and k=NoC−1). Cells in thesubframe boundary symbol for which k=0 or k=NoC−1 shall be edge pilots).Here, Dx may be 3, 4, 6, 8, 12, 16, 24, and 32, and the system mayselect one of these values depending on a channel environment. However,an edge pilot is inserted into a first carrier and a last carrier ofsubframe boundary symbols, respectively.

A position into which a continual pilot is to be inserted is defined byan index itself of carriers into which the continual pilot is inserted.

Specifically, the continual pilot may be inserted into differentpositions depending on an FFT size, and in an FFT size of 8K, an indexof carriers into which the continual pilot is to be inserted may bedefined as illustrated in following Table 3.

TABLE 3 59 167 307 469 637 751 865 1031 1159 1333 1447 1607 1811 19432041 2197 2323 2519 2605 2767 2963 3029 3175 3325 3467 3665 3833 39014073 4235 4325 4511 4627 4825 4907 5051 5227 5389 5531 5627 5833 59056053 6197 6353 6563 6637 6809

Accordingly, in a case where the FFT size is 8K, the system may insertthe continual pilot based on Table 3.

An edge pilot may be inserted into a first carrier and a last carrier ofthe symbols other than the preamble symbol, that is, a first carrier anda last carrier of OFDM symbols configuring a data symbols and subframeboundary symbols.

Meanwhile, carrier indices can be considered to be either absolutecarrier indices or relative carrier indices. Absolute carrier indicesare indexed on the maximum possible number of carriers regardless ofwhether carrier reduction has been configured and hence range from 0(i.e. an index of a first carrier) to NoC_(max)−1 (i.e. an index of alast carrier) (Here, NoC_(max)=6913). Relative carrier indices areindexed on the configured number of carriers and hence range from 0(i.e. an index of a first carrier) to NoC−1 (i.e. an index of a lastcarrier) (Here, NoC=6913, 6817, 6721, 6625 or 6529). Preamble,scattered, subframe boundary, and edge pilot locations depend on therelative carrier indices. Continual pilot locations depend on theabsolute carrier indices.

Meanwhile, in the case where at least one pilot is inserted as describedabove, a method for determining reserved tones according to an exemplaryembodiment will be described with reference to FIGS. 4 to 9.

First, indices for reserved tones are randomly selected. Here, theindices for the reserved tones represent carrier indices to be allocatedto the reserved tones. Meanwhile, the number of carriers N_(TR)allocated to the reserved tones may have different values depending onan FFT size. For example, in the case where an FFT size is 8K, N_(TR) is72 (N_(TR)=72).

Specifically, carrier indices for reserved tones are randomly selectedfrom among indices other than indices of carriers into which a pilot isinserted.

That is, the indices for the reserved tones are randomly selected(S410), and it is determined whether o the selected indices overlapindices of the pilot (S420), thereby making it possible to randomlyselect the carrier indices for the reserved tones among the indicesother than the indices of the carriers into which the pilot is inserted.

Here, the pilot may include a preamble pilot, a scattered pilot, asubframe boundary pilot, a continual pilot, and an edge pilot, and thepositions into which the respective pilots are inserted are as describedabove.

Thereafter, a kernel signal is generated based on the randomly selectedindices for the reserved tones. Specifically, in a case where therandomly selected indices do not overlap the indices of the pilot (No inS420), the kernel signal may be generated by inserting one (1) into thecarriers for the randomly selected indices and performing IFFT, as shownin FIG. 2 (S430).

In addition, a comparison reference average value of amplitudes of thekernel signal is calculated, the calculated comparison reference averagevalue is compared with a prestored comparison reference average value,and the indices of the reserved tones are preliminarily determined basedon the comparison.

Specifically, if the calculated comparison reference average value ofthe kernel signal is smaller than the prestored comparison referenceaverage value (Yes in S440), the prestored comparison reference averagevalue is replaced with the calculated comparison reference average value(S450). Here, the prestored comparison reference average value may be acomparison reference average value which is calculated and stored basedon randomly selected indices for the reserved tones, before performingthe above-mentioned processes. In this case, the randomly selectedindices for the reserved tones may also be stored, and in S450,prestored indices may also be updated.

In addition, if the comparison reference average value of the kernelsignal is smaller than a preset value (Yes in S460), the indices whichform the basis of the calculation of the comparison reference averagevalue may be preliminarily determined as indices of the reserved tonesto be used for PAPR reduction (S470).

That is, a smaller comparison reference average value among thecalculated comparison reference average value and the prestoredcomparison reference average value is compared with the preset value,and as a result of the comparison, if the comparison reference averagevalue is smaller than the preset value, indices which form the basis ofthe generation of the kernel signal having the comparison referenceaverage value are preliminarily determined as the indices of thereserved tones.

However, if the calculated comparison reference average value of thekernel signal is not smaller than the prestored comparison referenceaverage value, the indices of the reserved tones may be preliminarilydetermined by repeating the above-mentioned process until the calculatedcomparison reference average value becomes smaller than the prestoredcomparison reference average value, and determining whether thecalculated comparison reference average value is smaller than the presetvalue.

In addition, after the prestored comparison reference average value isreplaced with the calculated comparison reference average value, if thecomparison reference average value is greater than or equal to thepreset value, the indices for the reserved tones may be preliminarilydetermined by repeating the above-mentioned process until the comparisonreference average value becomes smaller than the preset value.

According to an exemplary embodiment, the comparison reference averagevalue of the kernel signal is an average value of amplitudes of peaksignals which satisfy a predetermined condition, except a peak signalhaving the greatest amplitude, among a plurality of peak signals of thekernel signal generated based on the randomly selected indices for thereserved tones.

According to an exemplary embodiment, the predetermined condition may bea condition that the peak signals, except the peak signal having thegreatest amplitude of the kernel signal generated based on the randomlyselected indices for the reserved tones, belong to a predeterminedamplitude range (for example, within top 10%), and belong to anotherpredetermined amplitude range (for example, within top 20%) based onamplitude of a peak signal having the second-largest amplitude. However,the above-mentioned numerical values are merely examples.

Hereinafter, a method of calculating a comparison reference averagevalue will be described in more detail with reference to FIGS. 5 to 8.

First, it is assumed that a kernel signal generated based on randomlyselected indices for reserved tones is as illustrated in FIG. 5.Referring to FIG. 5, the kernel signal comprises a plurality of peaksignals having various amplitudes in a time domain. In this case, theplurality of peak signals of the kernel signal are classified dependingon amplitudes, and a histogram illustrating the number of peak signalsaccording to the amplitudes may be illustrated as in FIG. 6.

Thereafter, a comparison reference average value of a kernel signal maybe calculated based on the histogram as illustrated in FIG. 6.

Specifically, as illustrated in FIG. 7, a first group of peak signalswhich belong to within top 10% in order of amplitude among peak signalsother than a peak signal having the greatest amplitude (i.e., a firstpeak signal) is determined using the histogram. In addition, asillustrated in FIG. 8, a second group of peak signals having anamplitude of 80% or more of the amplitude of a peak signal which is thesecond-largest amplitude (i.e., a second peak signal) is determinedusing the histogram.

In addition, peak signals which commonly belong to the first and secondgroups are determined by comparing the peak signals that belong to thefirst group and the second group, respectively, and an average value ofamplitudes of the peak signals which commonly belong to the first andsecond groups is calculated. The calculated value as described above isa comparison reference average value for the randomly selected indicesfor the reserved tones.

As such, according to the present exemplary embodiment, the comparisonreference average value is calculated using the peak signals having theamplitude of a specific percentage or more based on the amplitude of thesecond peak signal while belonging to within a specific range in orderof amplitude, among the peak signals, and if the comparison referenceaverage value is smaller than the preset value, the indices which formthe basis of the calculation of the comparison reference average valueis preliminarily determined as the indices of the reserved tones.

Here, the preset value, which is a value obtained by simulation, may beset to a value which may prevent an occurrence of a new peak by the peaksignals other than the first peak signal among the plurality of peaksignals configuring the kernel signal, particularly, the peak signalshaving a specific amplitude or more including the second peak signal,when the kernel signal is added to a data signal in order to reduce aPAPR.

Meanwhile, if the carrier indices of the reserved tones arepreliminarily determined, carrier indices for the reserved tones may befinally determined using the preliminarily determined carrier indices. Adetailed description thereof will be provided with reference to FIG. 9.

First, an order of the preliminarily determined indices of the reservedtones is randomly re-arranged (S910). In this case, K may be set to zero(K=0) and N_nochange may be set to zero (N_nochange=0).

For example, in a case where the preliminarily determined indices of thereserved tones are ‘1, 4, 8, and 9’, an order of these indices may berandomly re-arranged such as ‘8, 1, 9, and 4’.

In addition, the randomly re-arranged indices are changed to otherindices, and kernel signals are generated based on the changed indices.Further, comparison reference average values of the kernel signals arecalculated and compared to one another, and as a result of thecomparison, indices based on which a kernel signal having the smallestcomparison reference average value is generated are finally determinedas indices of the reserved tones to be used for reduction of the PAPR ofthe data signal.

Specifically, a comparison reference average value may be calculatedwhile sequentially changing the respective indices included in therandomly re-arranged indices of the reserved tones to indices, amongcarrier indices, where a pilot is not positioned and the preliminarilydetermined reserved tones are not positioned, and indices for thesmallest comparison reference average value among the calculatedcomparison reference average values may be finally determined as theindices of the reserved tones to be used for reduction of the PAPR ofthe data signal.

To this end, first, an optimization for a K-th index among the randomlyre-arranged indices of the reserved tones is performed (S920).

Here, the optimization means a process of determining indices whichgenerate the smallest comparison reference average value, when thecomparison reference average value is calculated while sequentiallychanging the K-th index to other indices.

Specifically, the indices which generate the smallest comparisonreference average value may be determined by sequentially changing theK-th index among the randomly re-arranged indices of the reserved tonesto an index among the carrier indices in which the pilot is notpositioned and the preliminarily determined reserved tone is notpositioned, and calculating a comparison reference average valuewhenever the index is changed.

As in the example described above, it is assumed that the indices of thepreliminarily determined reserved tones are ‘1, 4, 8, and 9’, and astate in which the indices of the preliminarily determined reservedtones are randomly re-arranged is ‘8, 1, 9, and 4’. Here, it is assumedthat the number of carriers for one OFDM symbol is 10, and indices ofcarriers into which the pilot is inserted are ‘3 and 7’. However, thisis merely an example for convenience of explanation.

Specifically, in the way that K=0, a comparison reference average valuemay be calculated by sequentially changing an index 8, which is azero-th index (i.e. a first value among the randomly re-arranged indices‘8, 1, 9, and 4’) among the randomly re-arranged indices, that is, ‘8,1, 9, and 4’ to an index other than ‘3 and 7’, which are the indices inwhich the pilot is positioned, and ‘1, 9, and 4’, which are indices inwhich other reserved tones are positioned.

That is, in a case where the indices are ‘0, 1, 9, and 4’, a kernelsignal may be generated by inserting 1 into carriers of which indicesare 0, 1, 9, and 4, and performing IFFT, and a comparison referenceaverage value of the generated kernel signal may be calculated.Similarly, a comparison reference average value may also be calculatedfor a case where indices are ‘2, 1, 9, and 4’, ‘5, 1, 9, and 4’, ‘6, 1,9, and 4’, and ‘8, 1, 9, and 4’, respectively.

In addition, the comparison reference average value having the minimumvalue among the calculated comparison reference average values isdetermined, and it is determined whether the K-th index among indiceswhen the comparison reference average value has the minimum value ischanged (S930). That is, it is determined whether the K-th index whenthe comparison reference average value has the minimum value is a valuedifferent from the existing K-th index.

In the above-mentioned example, in a case where indices when thecomparison reference average value has the minimum value are ‘5, 1, 9,and 4’, it may be estimated that the zero-th index based on ‘8, 1, 9,and 4’ is changed from 8 to 5.

As such, if the K-th index is changed (Yes in S930), N_nochange is setto 0 (N_nochange=0) (S940) and K is set to (K+1) mod N_(TR) (K=(K+1) modN_(TR)) (S950), and the above-mentioned process is repeated for a (K+1)mod N_(TR)-th index for the indices (i.e., in the above-mentionedexample, ‘5, 1, 9, and 4’) in which the K-th index is changed. Here,N_(TR) is the number of carriers used for the reserved tones.

However, in the above-mentioned example, in a case where the indiceswhen the smallest comparison reference average value is generated are‘8, 1, 9, and 4’, it may be estimated that the zero-th index based on‘8, 1, 9, and 4’ is not changed.

As such, if the K-th index is not changed (No in S930), N_nochange isset to N_nochange+1 (N_nochange=N_nochange+1) (S960) and it isdetermined whether N_nochange=N_(TR) is satisfied (S970).

Accordingly, if N_nochange=N_(TR) is satisfied (Yes in S970), it isdetermined that K=0, an order of indices is randomly re-arranged (S980),and the above-mentioned process is repeated.

However, if N_nochange=N_(TR) is not satisfied (No in S970), it isdetermined whether N_nochange=2*N_(TR) is satisfied (S990).

Accordingly, if N_nochange=2*N_(TR) is not satisfied (No in S990), K isset to (K+1) mod NTR (K=(K+1) mod N_(TR)) (S995), and theabove-mentioned process is repeated. However, if N_nochange=2*N_(TR) issatisfied (Yes in S990), indices output from S990 are finally determinedas the indices for the reserved tones (S997).

In the case where the indices of the reserved tones are determinedaccording to the method as described above, and a PAPR reduction isperformed based on the determined indices of the reserved tones,amplitudes of a second peak signal and peak signals having the nextsequentially high amplitude in the kernel signal may be generallyreduced. Accordingly, since a difference between the second peak signaland the peak signals having the next sequentially high amplitude in thekernel signal is reduced, when the kernel signal is added to the datasignal in order to reduce a PAPR, a new peak may not occur.

Meanwhile, the indices of the reserved tones determined according to theabove-mentioned method are as illustrated in following Table 4 and Table5. That is, Table 4 and Table 5 illustrate a set of carriers reservedfor PAPR reduction in a case where an FFT size is 8K.

Specifically, Table 4 illustrates a set of carriers reserved for allsymbols except a preamble symbol and subframe boundary symbols in a casewhere Dx is 3 and Dx is 4. That is, Table 4 illustrates a set ofcarriers reserved for data symbols, and a preamble symbol and subframeboundary symbols except the case where Dx is 3 and Dx is 4.

Specifically, in a case where positions in data symbols into which ascattered pilot is to be inserted are defined based on a pilot insertionpattern Dx=3, 4, 6, 8, 12, 16, 24, and 32, and Dy=2 and 4, and an edgepilot is to be inserted into a first carrier and a last carrier in eachof the data symbols, and in a case where a position in a preamble symbolinto which a preamble pilot is to be inserted and a position in subframeboundary symbols into which a subframe boundary pilot is to be insertedare defined based on a pilot insertion pattern Dx=6, 8, 12, 16, 24, and32, and an edge pilot is to be inserted into a first carrier and a lastcarrier in each of the subframe boundary symbols, a set of carrier to bereserved for the preamble symbol, the subframe boundary symbols, and thedata symbols is as illustrated in Table 4.

Table 5 illustrates a set of carriers reserved for a preamble symbol andsubframe boundary symbols in a case in which Dx is 3 and Dx is 4.

Specifically, in a case in which a position in a preamble symbol intowhich a preamble pilot is to be inserted and a position in subframeboundary symbols into which a subframe boundary pilot is to be insertedare defined based on a pilot insertion pattern (Dx=3 and 4), and an edgepilot is to be inserted into a first carrier and a last carrier in eachof the subframe boundary symbols, a set for carriers reserved for thepreamble symbol and the subframe boundary symbols is as illustrated inTable 5.

That is, in Table 4 and Table 5, in the case of scattered pilots to beinserted into the data symbols, Dy is 2 and 4.

In addition, in Table 4, in the case of scattered pilots to be insertedinto the data symbols, Dx is 3, 4, 6, 8, 12, 16, 24, and 32, and inTable 4, in the case of preamble pilots and subframe boundary pilots tobe inserted into the preamble symbol and the subframe boundary symbols,Dx is 6, 8, 12, 16, 24, and 32. In addition, in Table 5, in the case ofpreamble pilots and subframe boundary pilots to be inserted into thepreamble symbol and the subframe boundary symbols, Dx is 3 and 4.

In addition, in Tables 4 and 5, an edge pilot is to be inserted into afirst carrier and a last carrier in each of the subframe boundarysymbols and the data symbols.

TABLE 4 FFT Size (Number of Reserved Tones) Tone Reservation CarrierIndices 8K 250, 386, 407, 550, 591, 717, 763, 787, 797, 839, 950, 1090,(72) 1105, 1199, 1738, 1867, 1903, 1997, 2114, 2260, 2356, 2427, 2428,2444, 2452, 2475, 2564, 2649, 2663, 2678, 2740, 2777, 2819, 2986, 3097,3134, 3253, 3284, 3323, 3442, 3596, 3694, 3719, 3751, 3763, 3836, 4154,4257, 4355, 4580, 4587, 4678, 4805, 5084, 5126, 5161, 5229, 5321, 5445,5649, 5741, 5746, 5885, 5918, 6075, 6093, 6319, 6421, 6463, 6511, 6517,6577

TABLE 5 FFT Size (Number of Reserved Tones) Tone Reservation CarrierIndices 8K 295, 329, 347, 365, 463, 473, 481, 553, 578, 602, 742, 749,(72) 829, 922, 941, 1115, 1123, 1174, 1363, 1394, 1402, 1615, 1657,1702, 1898, 1910, 1997, 2399, 2506, 2522, 2687, 2735, 3043, 3295, 3389,3454, 3557, 3647, 3719, 3793, 3794, 3874, 3898, 3970, 4054, 4450, 4609,4666, 4829, 4855, 4879, 4961, 4969, 5171, 5182, 5242, 5393, 5545, 5567,5618, 5630, 5734, 5861, 5897, 5987, 5989, 6002, 6062, 6074, 6205, 6334,6497

Meanwhile, for data symbols, carriers having carrier indices defined inTable 4 are reserved, and these index values are circular-shifted,thereby making it possible to define other carrier indices reserved forPAPR reduction. Here, an amount of circular-shifted index values may bedetermined by Dx and Dy.

Specifically, in a data symbol corresponding to an index 1, a set S₁ ofreserved carriers may be calculated based on following mathematicalexpression 2.

S ₁ =i _(k) +D _(X)*(I mod D _(Y)), i _(n) ∈ S ₀, 0≦n<N _(TR) , d ₀ ≦|<d_(end)   (2)

Here, S₀ represents a set of reserved carriers corresponding to carrierindices defined in Table 4, N_(TR) represents the number of cellsreserved per an OFDM symbol, d₀ represents indices of a first OFDMsymbol of a subframe, and d_(end) represents an index of the last datasymbol.

In the meantime, when a position where a preamble pilot is inserted inthe preamble symbol and a position where a sub frame boundary pilot isinserted in the sub frame boundary symbols are defined based on pilotinsertion pattern Dx=6,8,12,16,24,32, the set of carriers to be reservedfor the preamble symbols and the sub frame boundary symbols are as shownin Table 4.

In the meantime, other than the above, even in the case where a positionwhere a preamble pilot is inserted in the preamble symbol and a positionwhere a sub frame boundary pilot is inserted in the sub frame boundarysymbols are defined based on pilot insertion pattern Dx=6, 12, 16, 24,32, the set of carriers to be reserved for the preamble symbols and thesub frame boundary symbols are as described in Table 4.

In this case, when a position where a preamble pilot is inserted in thepreamble symbol and a position where a sub frame boundary pilot isinserted in the sub frame boundary symbols are defined based Dx=3, 4, 8,the set of carriers to be reserved for the preamble symbols and the subframe boundary symbols are as described in Table 5.

FIG. 10 is a flowchart illustrating a method of determining reservedtones according to an exemplary embodiment.

First, indices of reserved tones are randomly selected, and a kernelsignal is generated based on the randomly selected indices (S1010).

Thereafter, a comparison reference average value of the generated kernelsignal is calculated, the calculated comparison reference average valueis compared with a prestored comparison reference average value, andindices of the reserved tones are preliminarily determined (S1020).

In addition, the order of the preliminarily determined indices of thereserved tones is randomly re-arranged (S1030), a comparison referenceaverage value is calculated while changing each of the randomlyre-arranged indices of the reserved tones, and indices which forms abasis of the smallest comparison reference average value are finallydetermined as indices of the reserved tones (S1040).

Here, in S1010, a kernel signal may be generated by randomly selectingcarrier indices for the reserved tones among indices other than carrierindices into which a pilot is inserted, inserting 1 into carriers of therandomly selected indices, and performing IFFT.

The comparison reference average value of the kernel signal is anaverage value of amplitudes of peak signals which satisfy apredetermined condition, except a peak signal having the greatestamplitude, among a plurality of peak signals of the kernel signalgenerated based on the randomly selected indices for the reserved tones.The predetermined condition may be a condition that the peak signalsbelong to a predetermined top range based on amplitude, except the peaksignal having the greatest amplitude, among the plurality of peaksignals of the kernel signal, and belong to another predetermined toprange based on amplitude of a peak signal having the second-largestamplitude.

In S1020, a smaller comparison reference average value among thecalculated comparison reference average value and the prestoredcomparison reference average value may be compared with a preset value,and indices for the kernel signal having a comparison reference averagevalue smaller than the preset value may be preliminarily determined asindices of the reserved tones.

In addition, in S1040, the comparison reference average value may becalculated while sequentially changing the respective indices includedin the randomly re-arranged indices of the reserved tones to indices,among indices of carries, where a pilot is not positioned and thepreliminarily determined reserved tones are not positioned, and indiceswhich generate the smallest comparison reference average value among thecalculated comparison reference average values may be finally determinedas indices of the reserved tones to be used for reduction of the PAPR ofthe data signal.

Meanwhile, the method for determining the carrier indices for thereserved tones is as described above.

Meanwhile, according to the present exemplary embodiments, the carrierindices defined as illustrated in Table 4 and Table 5 may be reservedfor the reserved tones and a PAPR of a data signal may be reduced usingthe reserved carrier indices, so as to be transmitted to a receiver.

FIG. 11 is a block diagram illustrating a configuration of a transmitteraccording to an exemplary embodiment.

Referring to FIG. 11, a transmitter 1100 includes a frame generator1110, a pilot inserter 1120, and a PAPR reducer 1130.

The frame generator 1110 generates a frame. Specifically, the framegenerator may generate a frame including a plurality of OFDM symbolshaving an FFT size of 8K.

Here, the frame includes a preamble symbol, subframe boundary symbols,and data symbols, and a detailed structure thereof is as illustrated inFIG. 3.

In this case, the frame generator 1110 may insert an L1 signaling andbroadcast data into the symbols by considering a position into which apilot is to be inserted and positions of reserved tones.

Specifically, the frame is constituted by carriers in a frequency domainand an integer number of OFDM symbols in a time domain. In this case,the frame generator 1110 may insert the L1 signaling into carriers amonga plurality of carriers of the preamble symbol in which the pilot andthe reserved tones are not to be positioned, and may insert thebroadcast data into carriers among a plurality of carriers of thesubframe symbols in which the pilot and the reserved tones are not to bepositioned. Meanwhile, the carriers into which the pilot is to beinserted and the carriers reserved for PAPR reduction are as describedabove.

The pilot inserter 1120 inserts the pilot into the frame. Specifically,the pilot inserter 1120 may insert the pilot into first carriers of theplurality of OFDM symbols, respectively.

In this case, the pilot may include a preamble pilot, a continual pilot,a subframe boundary pilot, a scattered pilot, and an edge pilot.

Accordingly, the pilot inserter 1120 may insert the preamble pilot andthe continual pilot into the preamble symbol, may insert the subframeboundary pilot, the continual pilot, and the edge pilot into thesubframe boundary symbols, and may insert the scattered pilot, thecontinual pilot, and the edge pilot into the data symbols.

Here, the pilot inserter 1120 may determine a position into which thepilot is to be inserted based on a specific pilot pattern (e.g., Dx andDy) predefined in a system, or based on carrier indices predefined inthe system. Meanwhile, the position into which the pilot is to beinserted depending on a pilot type is as described above.

The PAPR reducer 1130 performs PAPR reduction using reserved tones.Specifically, the PAPR reducer 1130 may insert a signal for reducingPAPR into second carriers reserved in at least one of the plurality ofOFDM symbols into which the pilot is inserted. That is, the PAPR reducer1130 may insert a tone reservation signal (e.g., cells which do notinclude data and L1 signaling) into carriers reserved for PAPRreduction, in order to reduce a PAPR of an output waveform.

To this end, the transmitter 1100 may further include an IFFT unit (notillustrated) for performing IFFT on the data and the frame into whichthe pilot is inserted in a frequency domain to generate a signal of atime domain.

In this case, the PAPR reducer 1130 may use a gradient algorithm, asdescribed above with reference to FIG. 1. However, this is merely oneexample, and the PAPR reducer 1130 may use various algorithms accordingto a tone reservation method.

Meanwhile, the second reserved carriers may be defined as illustrated inTable 4 and Table 5.

For example, the second reserved carriers have carrier indices definedas in Table 4, when a position in a preamble symbol into which apreamble pilot is to be inserted and a position in subframe boundarysymbols into which a subframe boundary pilot is to be inserted aredefined based on a pilot insertion pattern (Dx=6, 8, 12, 16, 24, 32),and an edge pilot is to be inserted into a first carrier and a lastcarrier in each of the subframe boundary symbols.

In addition, the second reserved carriers have carrier indices definedas illustrated in Table 4 in data symbols, in a case in which a positioninto which a scattered pilot is to be inserted is defined based on apilot insertion pattern (Dx=3, 4, 6, 8, 12, 16, 24, 32 and Dy=2, 4), andan edge pilot is to be inserted into a first carrier and a last carrierin each of the data symbols.

Meanwhile, the second reserved carriers have carrier indices defined asin Table 5, when a position in a preamble symbol into which a preamblepilot is to be inserted and a position in subframe boundary symbols intowhich a subframe boundary pilot is to be inserted are defined based on apilot insertion pattern (Dx=3 and 4), and an edge pilot is to beinserted into a first carrier and a last carrier in each of the subframeboundary symbols.

Here, Dx is a difference of carrier indices between adjacent carriersinto which a pilot is to be inserted, and Dy is a difference of symbolindices between successive pilots on a specific carrier.

As such, the transmitter 1100 may perform PAPR reduction using thereserved tones and may transmit a signal of which a PAPR is reduced to areceiver (not illustrated).

Meanwhile, the transmitter 1100 may further include components otherthan the components illustrated in FIG. 11.

For example, the transmitter 1100 may further include components forencoding and modulating the data and the L1 signaling.

Specifically, the transmitter 110 may further include an encoder (notillustrated) for encoding the broadcast data and the L1 signaling, a bitinterleaver (not illustrated) for interleaving the encoded broadcastdata and L1 signaling, a constellation mapper (not illustrated) formapping the interleaved broadcast data and L1 signaling to constellationto generate a modulated symbol, and a time interleaver (not illustrated)and a frequency interleaver (not illustrated) for interleaving thebroadcast data and the L1 signaling in a time domain and a frequencydomain, respectively.

In addition, the transmitter 1100 may further include an IFFT unit (notillustrated) which performs IFFT for the broadcast data, the L1signaling, and the frame into which the pilot is inserted, and mayfurther include a guard interval inserter (not illustrated) forinserting a guard interval into a signal that the PAPR reduction isperformed, a bootstrap unit (not illustrated) for inserting informationon the L1 signaling into bootstrap symbols after the guard interval isinserted, and a transmitting unit (not illustrated) for up-converting asignal into which the bootstrap symbols are inserted into a signal of aradio frequency (RF) band and transmitting the up-converted signal to areceiving side.

FIG. 12 is a block diagram illustrating a configuration of a receiveraccording to an exemplary embodiment.

Referring to FIG. 12, a receiver 1200 includes a receiving unit 1210, areserved tone remover 1220, and a signal processor 1230.

The receiving unit 1210 receives a frame transmitted from thetransmitter 1100. Specifically, the receiving unit 1210 may synchronizethe frame, may receive the signal through an allocated frequency band,and may down-convert a received RF band signal into a baseband signal.In addition, the receiving unit 1210 may perform a Fast FourierTransform (FFT) to restore symbols mapped to the frequency domain. Thatis, the receiving unit 1210 may restore a plurality of OFDM symbolsmapped to the frame.

The reserved tone remover 1220 removes reserved tones from a pluralityof OFDM symbols constituting the frame.

Specifically, the reserved tone remover 1220 determines positions of thereserved tones in the symbols and removes the reserved tones from thecorresponding positions. Accordingly, the reserved tone remover 1220 mayremove the reserved tones and may extract only data.

Here, information on the carrier indices allocated for the reservedtones may be prestored in the receiver 1200, or may be provided from thetransmitter 1100. Meanwhile, the carrier indices allocated for thereserved tones are as illustrated in the Table 4 and Table 5 describedabove.

The signal processor 1230 processes a plurality of OFDM symbols fromwhich the reserved tones are removed. That is, the signal processor 1230may process data received as the reserved tones are removed.

Specifically, the signal processor 1230 may deinterleave the broadcastdata and the L1 signaling in the frequency domain and the time domainusing a frequency deinterleaver (not illustrated) and a timedeinterleaver (not illustrated), may extract the signal mapped to theconstellation using a constellation demapper (not illustrated), maydeinterleave and decode the broadcast data and the L1 signaling using abit deinterleaver (not illustrated) and a decoder (not illustrated), andmay restore the broadcast data and the L1 signaling. In this case,because the L1 signaling includes signaling information on the broadcastdata, the L1 signaling may be used upon restoring the broadcast data.

FIG. 13 is a flowchart illustrating a method for inserting a reservedtone signal according to an exemplary embodiment of the presentdisclosure.

First, a frame including a plurality of OFDM symbols having an FFT sizeof 8K is generated (S1310).

Thereafter, a pilot is inserted into first carriers of the plurality ofOFDM symbols, respectively (S1320).

In addition, a signal for reducing a PAPR is inserted into secondcarriers reserved in at least one of the plurality of OFDM symbols intowhich the pilot is inserted (S1330).

Here, the frame includes the preamble symbol, the subframe boundarysymbols, and the data symbols.

In this case, the second reserved carriers may have the carrier indicesdefined as in Table 4 and Table 5.

The second reserved carriers have the carrier indices defined as inTable 4, when a position in the preamble symbol into which a preamblepilot is to be inserted and a position in the subframe boundary symbolsinto which a subframe boundary pilot is to be inserted are defined basedon a pilot insertion pattern (Dx=6, 8, 12, 16, 24, 32), and an edgepilot is to be inserted into a first carrier and a last carrier in eachof the subframe boundary symbols. In addition, the second carriersreserved have the carrier indices defined as illustrated in Table 4 inthe data symbols, in the case where a position into which a scatteredpilot is to be inserted is determined based on a pilot insertion pattern(Dx=3, 4, 6, 8, 12, 16, 24, 32 and Dy=2, 4), and an edge pilot is to beinserted into a first carrier and a last carrier in each of the datasymbols.

In addition, the second reserved carriers have the carrier indicesdefined as in Table 5, when a position in the preamble symbol into whicha preamble pilot is to be inserted and a position in subframe boundarysymbols into which a subframe boundary pilot is to be inserted aredefined based on Dx=3 and 4, and an edge pilot is to be inserted into afirst carrier and a last carrier in each of the subframe boundarysymbols.

Here, Dx is a difference of carrier indices between adjacent carriersinto which the pilot is to be inserted, and Dy is a difference of symbolindices between successive pilots on a specific carrier.

Meanwhile, a non-transitory computer readable medium having a programstored therein may be provided, wherein the program sequentiallyperforms the method for determining reserved tones according to theexemplary embodiments.

The non-transitory computer readable medium does not mean a mediumstoring data for a short period such as a register, a cache, a memory,or the like, but means a machine-readable medium semi-permanentlystoring the data. Specifically, various applications or programsdescribed above may be stored and provided in the non-transitorycomputer readable medium such as a compact disc (CD), a digitalversatile disk (DVD), a hard disk, a Blu-ray disk, a universal serialbus (USB), a memory card, a read-only memory (ROM), or the like.

In addition, although a bus is not illustrated in the block diagramillustrating the transmitter and the receiver, communications betweenthe respective components in the transmitter and the receiver may alsobe performed via the bus. In addition, the respective apparatuses mayfurther include a processor such as a central processing unit (CPU), amicroprocessor, or the like which performs various operations describedabove, and may further include a memory for performing various operationdescribed above.

A term “module”, “unit” “part”, or the like as represented by a block inFIGS. 1, 11 and 12, in the exemplary embodiments, is a term forreferring to the component performing at least one function oroperation, and such component may be implemented in hardware or softwareor a combination of hardware and software. In addition, a plurality of“modules”, “units”, “parts”, or the like may be integrated into at leastone module or chip and may be implemented in or by at least oneprocessor (not illustrated) such as a microprocessor, except for a casein which they need to be each implemented in individual specifichardware.

Hereinabove, although the exemplary embodiments have been shown anddescribed, it should be understood that the inventive concept is notlimited to the disclosed embodiments and may be variously changedwithout departing from the spirit and the scope of the inventiveconcept. Therefore, the exemplary embodiments should be construed asincluding all the changes, equivalents, and substitutions included inthe spirit and scope of the present disclosure.

What is claimed is:
 1. A method of determining reserved tones to be usedfor reduction of a peak to average power ratio (PAPR) of a signal, themethod comprising: randomly selecting carrier indices for the reservedtones and generating a kernel signal based on the randomly selectedcarrier indices for the reserved tones; calculating a comparisonreference average value of the kernel signal, comparing the calculatedcomparison reference average value with a prestored comparison referenceaverage value, and preliminarily determining carrier indices of thereserved tones based on the comparison; re-arranging an order of thepreliminarily determined carrier indices of the reserved tones;calculating comparison reference average values of kernel signalsgenerated by changing each of the re-arranged carrier indices of thereserved tones to another carrier index, and finally determining carrierindices of the reserved tones which generate a kerneal signal having thesmallest comparison reference average value among the comparisonreference average values as carrier indices of the reserved tones to beused for the reduction of the PAPR.
 2. The method as claimed in claim 1,wherein the generating the kernel signal based on the randomly selectedcarrier indices for the reserved tones, the kernel signal is generatedby randomly selecting carrier indices for the reserved tones amongcarrier indices other than carrier indices into which a pilot isinserted, inserting one (1) into carriers of the randomly selectedcarrier indices, and performing Inverse Fast Fourier Transform (IFFT) onthe carriers into which one (1) is inserted.
 3. The method as claimed inclaim 1, wherein the comparison reference average value of the kernelsignal is an average value of amplitudes of peak signals satisfying apredetermined condition, except a peak signal having the greatestamplitude, among the plurality of peak signals of the kernel signal. 4.The method as claimed in claim 3, wherein the predetermined condition isa condition that the peak signals belong to a predetermined top range ofamplitude except the peak signal having the greatest amplitude andanother predetermined top range of amplitude based on an amplitude of apeak signal having the second-largest amplitude, among the plurality ofpeak signals of the kernel signal.
 5. The method as claimed in claim 1,wherein in the preliminarily determining the carrier indices of thereserved tones, a smaller comparison reference average value among thecalculated comparison reference average value and the prestoredcomparison reference average value is compared with a preset value, andcarrier indices for a kernel signal having the smaller comparisonreference average value which is smaller than the preset value ispreliminarily determined as the indices of the reserved tones.
 6. Themethod as claimed in claim 1, wherein the comparison reference averagevalues are calculated by sequentially changing respective carrierindices included in the re-arranged carrier indices of the reservedtones to other carrier indices where a pilot is not positioned and thepreliminarily determined reserved tones are not positioned.
 7. Atransmitter comprising: a frame generator configured to generate a frameincluding a plurality of Orthogonal Frequency Division Multiplexing(OFDM) symbols having a Fast Fourier Transform (FFT) size of 8K; a pilotinserter configured to insert a pilot into first carriers of theplurality of OFDM symbols, respectively; and a peak to average powerratio (PAPR) reducer configured to insert a signal for reducing a PAPRinto second carriers reserved in at least one of the plurality of OFDMsymbols into which the pilot is inserted, wherein the second carriershave carrier indices defined as follows. FFT Size (Number of ReservedTones) Carrier Indices 8K 250, 386, 407, 550, 591, 717, 763, 787, 797,839, 950, 1090, (72) 1105, 1199, 1738, 1867, 1903, 1997, 2114, 2260,2356, 2427, 2428, 2444, 2452, 2475, 2564, 2649, 2663, 2678, 2740, 2777,2819, 2986, 3097, 3134, 3253, 3284, 3323, 3442, 3596, 3694, 3719, 3751,3763, 3836, 4154, 4257, 4355, 4580, 4587, 4678, 4805, 5084, 5126, 5161,5229, 5321, 5445, 5649, 5741, 5746, 5885, 5918, 6075, 6093, 6319, 6421,6463, 6511, 6517, 6577


8. The transmitter as claimed in claim 7, wherein the frame includes apreamble symbol, subframe boundary symbols, and data symbols.
 9. Thetransmitter as claimed in claim 8, wherein the second carriers have thecarrier indices, when a position in the preamble symbol into which apreamble pilot is to be inserted and a position in the subframe boundarysymbols into which a subframe boundary pilot is to be inserted aredefined based on a pilot insertion pattern, and an edge pilot is to beinserted into a first carrier and a last carrier in each of the subframeboundary symbols.
 10. The transmitter as claimed in claim 9, wherein thepilot insertion pattern is determined based on Dx=6, 12, 16, 24, 32, andwherein Dx is a difference of carrier indices between adjacent carriersinto which the pilot is to be inserted.
 11. The transmitter as claimedin claim 8, wherein the second carriers have the carrier indices, when aposition in the data symbols into which a scattered pilot is to beinserted are defined based on a pilot insertion pattern, and an edgepilot is to be inserted into a first carrier and a last carrier in eachof the data symbols.
 12. The transmitter as claimed in claim 11, whereinthe pilot insertion pattern is determined based Dx=3, 4, 6, 8, 12, 16,24, 32, and wherein Dx is a difference of carrier indices betweenadjacent carriers into which the pilot is to be inserted.
 13. Thetransmitter as claimed in claim 11, wherein the pilot insertion patternis determined based Dy=2, 4, and wherein Dy is a difference of symbolindices between successive pilots on a specific carrier.
 14. Atransmitter comprising: a frame generator configured to generate a frameincluding a plurality of Orthogonal Frequency Division Multiplexing(OFDM) symbols having a Fast Fourier Transform (FFT) size of 8K; a pilotinserter configured to insert a pilot into first carriers of theplurality of OFDM symbols, respectively; and a peak to average powerratio (PAPR) reducer configured to insert a signal for reducing a PAPRinto second carriers reserved in at least one of the plurality of OFDMsymbols into which the pilot is inserted, wherein the second carriershave carrier indices defined as follows. FFT Size (Number of ReservedTones) Carrier Indices 8K 295, 329, 347, 365, 463, 473, 481, 553, 578,602, 742, 749, (72) 829, 922, 941, 1115, 1123, 1174, 1363, 1394, 1402,1615, 1657, 1702, 1898, 1910, 1997, 2399, 2506, 2522, 2687, 2735, 3043,3295, 3389, 3454, 3557, 3647, 3719, 3793, 3794, 3874, 3898, 3970, 4054,4450, 4609, 4666, 4829, 4855, 4879, 4961, 4969, 5171, 5182, 5242, 5393,5545, 5567, 5618, 5630, 5734, 5861, 5897, 5987, 5989, 6002, 6062, 6074,6205, 6334, 6497


15. The transmitter as claimed in claim 14, wherein the frame includes apreamble symbol, subframe boundary symbols, and data symbols.
 16. Thetransmitter as claimed in claim 15, wherein the second carriers have thecarrier indices, when a position in the preamble symbol into which apreamble pilot is to be inserted and a position in the subframe boundarysymbols into which a subframe boundary pilot is to be inserted aredefined based on a pilot insertion pattern, and an edge pilot is to beinserted into a first carrier and a last carrier in each of the subframeboundary symbols.
 17. The transmitter as claimed in claim 16, whereinthe pilot insertion pattern is determined based Dx=3, 4, and wherein Dxis a difference of carrier indices between adjacent carriers into whichthe pilot is to be inserted.